diff --git a/conf/boards/classix.makefile b/conf/boards/classix.makefile
index 52e64bc6cb..36a8ee3d14 100644
--- a/conf/boards/classix.makefile
+++ b/conf/boards/classix.makefile
@@ -12,9 +12,8 @@ BOARD_VERSION=1.0
 
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 
 LPC21ISP_BAUD = 38400
@@ -44,9 +43,4 @@ GPS_BAUD ?= B38400
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_pwm
-endif
-
-
-
+ACTUATORS ?= actuators_pwm
diff --git a/conf/boards/lia_1.1.makefile b/conf/boards/lia_1.1.makefile
index 8fab3655c1..40a844386e 100644
--- a/conf/boards/lia_1.1.makefile
+++ b/conf/boards/lia_1.1.makefile
@@ -65,9 +65,7 @@ GPS_BAUD ?= B38400
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_pwm
-endif
+ACTUATORS ?= actuators_pwm
 
 
 ifndef ADC_IR1
@@ -82,6 +80,4 @@ ifndef ADC_IR3
 ADC_IR_TOP      = 3
 ADC_IR_TOP_CHAN = 2
 endif
-ifndef ADC_IR_NB_SAMPLES
-ADC_IR_NB_SAMPLES = 16
-endif
+ADC_IR_NB_SAMPLES ?= 16
diff --git a/conf/boards/lisa_l_1.0.makefile b/conf/boards/lisa_l_1.0.makefile
index 17578ee3bf..fd49fb70c4 100644
--- a/conf/boards/lisa_l_1.0.makefile
+++ b/conf/boards/lisa_l_1.0.makefile
@@ -28,9 +28,8 @@ else
 endif
 # -----------------------------------------------------------------------
 
-ifndef FLASH_MODE
-FLASH_MODE = JTAG
-endif
+# default flash mode is the onboard JTAG
+FLASH_MODE ?= JTAG
 
 #
 #
@@ -41,50 +40,24 @@ endif
 #
 # default LED configuration
 #
-ifndef RADIO_CONTROL_LED
-RADIO_CONTROL_LED  = 5
-endif
-
-ifndef BARO_LED
-BARO_LED = none
-endif
-
-ifndef AHRS_ALIGNER_LED
-AHRS_ALIGNER_LED = 7
-endif
-
-ifndef GPS_LED
-GPS_LED = 3
-endif
-
-ifndef SYS_TIME_LED
-SYS_TIME_LED = 1
-endif
+RADIO_CONTROL_LED  ?= 5
+BARO_LED           ?= none
+AHRS_ALIGNER_LED   ?= 7
+GPS_LED            ?= 3
+SYS_TIME_LED       ?= 1
 
 
 #
 # default uart configuration
 #
-ifndef RADIO_CONTROL_SPEKTRUM_PRIMARY_PORT
-RADIO_CONTROL_SPEKTRUM_PRIMARY_PORT   = UART3
-endif
-ifndef RADIO_CONTROL_SPEKTRUM_SECONDARY_PORT
-RADIO_CONTROL_SPEKTRUM_SECONDARY_PORT = UART5
-endif
+RADIO_CONTROL_SPEKTRUM_PRIMARY_PORT   ?= UART3
+RADIO_CONTROL_SPEKTRUM_SECONDARY_PORT ?= UART5
 
-ifndef MODEM_PORT
-MODEM_PORT=UART2
-endif
-ifndef MODEM_BAUD
-MODEM_BAUD=B57600
-endif
+MODEM_PORT ?= UART2
+MODEM_BAUD ?= B57600
 
-ifndef GPS_PORT
-GPS_PORT=UART1
-endif
-ifndef GPS_BAUD
-GPS_BAUD=B38400
-endif
+GPS_PORT ?= UART1
+GPS_BAUD ?= B38400
 
 #
 # default actuator configuration
@@ -92,9 +65,7 @@ endif
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_pwm
-endif
+ACTUATORS ?= actuators_pwm
 
 
 ifndef ADC_IR1
@@ -109,6 +80,4 @@ ifndef ADC_IR3
 ADC_IR_TOP      = 4
 ADC_IR_TOP_CHAN = 3
 endif
-ifndef ADC_IR_NB_SAMPLES
-ADC_IR_NB_SAMPLES = 16
-endif
+ADC_IR_NB_SAMPLES ?= 16
diff --git a/conf/boards/lisa_l_1.1.makefile b/conf/boards/lisa_l_1.1.makefile
index 12880072c3..ea380d68f2 100644
--- a/conf/boards/lisa_l_1.1.makefile
+++ b/conf/boards/lisa_l_1.1.makefile
@@ -31,9 +31,8 @@ else
 endif
 # -----------------------------------------------------------------------
 
-ifndef FLASH_MODE
-FLASH_MODE = JTAG
-endif
+# default flash mode is the onboard JTAG
+FLASH_MODE ?= JTAG
 
 #
 #
@@ -72,9 +71,7 @@ GPS_BAUD ?= B38400
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_pwm
-endif
+ACTUATORS ?= actuators_pwm
 
 
 ifndef ADC_IR1
@@ -89,6 +86,4 @@ ifndef ADC_IR3
 ADC_IR_TOP      = 4
 ADC_IR_TOP_CHAN = 3
 endif
-ifndef ADC_IR_NB_SAMPLES
-ADC_IR_NB_SAMPLES = 16
-endif
+ADC_IR_NB_SAMPLES ?= 16
diff --git a/conf/boards/lisa_m_1.0.makefile b/conf/boards/lisa_m_1.0.makefile
index e56f73bd66..fd8c902767 100644
--- a/conf/boards/lisa_m_1.0.makefile
+++ b/conf/boards/lisa_m_1.0.makefile
@@ -21,10 +21,9 @@ $(TARGET).LDSCRIPT=$(SRC_ARCH)/lisa-m.ld
 
 # -----------------------------------------------------------------------
 
-ifndef FLASH_MODE
-FLASH_MODE = JTAG
-#FLASH_MODE = SERIAL
-endif
+# default flash mode is JTAG
+# other possibilities: SWD, SERIAL
+FLASH_MODE ?= JTAG
 
 #
 #
@@ -62,9 +61,7 @@ GPS_BAUD ?= B38400
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_pwm
-endif
+ACTUATORS ?= actuators_pwm
 
 
 ifndef ADC_IR1
@@ -79,6 +76,4 @@ ifndef ADC_IR3
 ADC_IR_TOP      = 3
 ADC_IR_TOP_CHAN = 2
 endif
-ifndef ADC_IR_NB_SAMPLES
-ADC_IR_NB_SAMPLES = 16
-endif
+ADC_IR_NB_SAMPLES ?= 16
diff --git a/conf/boards/lisa_m_2.0.makefile b/conf/boards/lisa_m_2.0.makefile
index 73ed8173d6..f73023a06c 100644
--- a/conf/boards/lisa_m_2.0.makefile
+++ b/conf/boards/lisa_m_2.0.makefile
@@ -18,11 +18,9 @@ $(TARGET).LDSCRIPT=$(SRC_ARCH)/lisa-m.ld
 
 # -----------------------------------------------------------------------
 
-ifndef FLASH_MODE
-FLASH_MODE = DFU
-#FLASH_MODE = JTAG
-#FLASH_MODE = SERIAL
-endif
+# default flash mode is via usb dfu bootloader (luftboot)
+# other possibilities: JTAG, SWD, SERIAL
+FLASH_MODE ?= DFU
 
 ifndef NO_LUFTBOOT
 $(TARGET).CFLAGS+=-DLUFTBOOT
@@ -65,9 +63,7 @@ GPS_BAUD ?= B38400
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_pwm
-endif
+ACTUATORS ?= actuators_pwm
 
 
 ifndef ADC_IR1
@@ -82,6 +78,4 @@ ifndef ADC_IR3
 ADC_IR_TOP      = 3
 ADC_IR_TOP_CHAN = 2
 endif
-ifndef ADC_IR_NB_SAMPLES
-ADC_IR_NB_SAMPLES = 16
-endif
+ADC_IR_NB_SAMPLES ?= 16
diff --git a/conf/boards/tiny_0.99.makefile b/conf/boards/tiny_0.99.makefile
index a87b5487fe..b5a98c386f 100644
--- a/conf/boards/tiny_0.99.makefile
+++ b/conf/boards/tiny_0.99.makefile
@@ -11,11 +11,8 @@ BOARD_VERSION=0.99
 
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
-
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
-
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 LPC21ISP_BAUD = 38400
 LPC21ISP_XTAL = 12000
@@ -41,22 +38,19 @@ GPS_BAUD ?= B38400
 
 
 
-ADC_IR_TOP = ADC_0
-ADC_IR1 = ADC_1
-ADC_IR2 = ADC_2
-ADC_IR_NB_SAMPLES = 16
-ADC_GYRO_NB_SAMPLES = 16
+ADC_IR_TOP ?= ADC_0
+ADC_IR1 ?= ADC_1
+ADC_IR2 ?= ADC_2
+ADC_IR_NB_SAMPLES ?= 16
+ADC_GYRO_NB_SAMPLES ?= 16
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4015
-endif
-
+ACTUATORS ?= actuators_4015
 
 # All targets on the TINY board run on the same processor achitecture
 $(TARGET).ARCHDIR = $(ARCH)
diff --git a/conf/boards/tiny_1.1.makefile b/conf/boards/tiny_1.1.makefile
index a84cd3bba5..c5ca642a9d 100644
--- a/conf/boards/tiny_1.1.makefile
+++ b/conf/boards/tiny_1.1.makefile
@@ -11,10 +11,8 @@ BOARD_VERSION=1.1
 
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
-
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 
 LPC21ISP_BAUD = 38400
@@ -40,21 +38,19 @@ GPS_PORT ?= UART1
 GPS_BAUD ?= B38400
 
 
-ADC_IR_TOP = ADC_0
-ADC_IR1 = ADC_1
-ADC_IR2 = ADC_2
-ADC_IR_NB_SAMPLES = 16
-ADC_GYRO_NB_SAMPLES = 16
+ADC_IR_TOP ?= ADC_0
+ADC_IR1 ?= ADC_1
+ADC_IR2 ?= ADC_2
+ADC_IR_NB_SAMPLES ?= 16
+ADC_GYRO_NB_SAMPLES ?= 16
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4015
-endif
+ACTUATORS ?= actuators_4015
 
 
 # All targets on the TINY board run on the same processor achitecture
diff --git a/conf/boards/tiny_2.1.makefile b/conf/boards/tiny_2.1.makefile
index 04ae4c8012..fc95ecf526 100644
--- a/conf/boards/tiny_2.1.makefile
+++ b/conf/boards/tiny_2.1.makefile
@@ -11,10 +11,8 @@ BOARD_VERSION=2.1
 
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
-
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 
 LPC21ISP_BAUD = 38400
@@ -40,22 +38,19 @@ GPS_PORT ?= UART0
 GPS_BAUD ?= B38400
 
 
-ADC_IR_TOP = ADC_0
-ADC_IR1 = ADC_1
-ADC_IR2 = ADC_2
-ADC_IR_NB_SAMPLES = 16
-ADC_GYRO_NB_SAMPLES = 16
+ADC_IR_TOP ?= ADC_0
+ADC_IR1 ?= ADC_1
+ADC_IR2 ?= ADC_2
+ADC_IR_NB_SAMPLES ?= 16
+ADC_GYRO_NB_SAMPLES ?= 16
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4017
-endif
-
+ACTUATORS ?= actuators_4017
 
 # All targets on the TINY board run on the same processor achitecture
 $(TARGET).ARCHDIR = $(ARCH)
diff --git a/conf/boards/tiny_2.11.makefile b/conf/boards/tiny_2.11.makefile
index d1d2702460..8f0c649ebf 100644
--- a/conf/boards/tiny_2.11.makefile
+++ b/conf/boards/tiny_2.11.makefile
@@ -12,9 +12,8 @@ BOARD_VERSION=2.11
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
 
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 
 LPC21ISP_BAUD = 38400
@@ -40,21 +39,19 @@ GPS_PORT ?= UART0
 GPS_BAUD ?= B38400
 
 
-ADC_IR_TOP = ADC_0
-ADC_IR1 = ADC_1
-ADC_IR2 = ADC_2
-ADC_IR_NB_SAMPLES = 16
-ADC_GYRO_NB_SAMPLES = 16
+ADC_IR_TOP ?= ADC_0
+ADC_IR1 ?= ADC_1
+ADC_IR2 ?= ADC_2
+ADC_IR_NB_SAMPLES ?= 16
+ADC_GYRO_NB_SAMPLES ?= 16
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4017
-endif
+ACTUATORS ?= actuators_4017
 
 
 # All targets on the TINY board run on the same processor achitecture
diff --git a/conf/boards/twog_1.0.makefile b/conf/boards/twog_1.0.makefile
index 5d5f8fc349..572bb95217 100644
--- a/conf/boards/twog_1.0.makefile
+++ b/conf/boards/twog_1.0.makefile
@@ -11,10 +11,8 @@ BOARD_VERSION=1.0
 
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
-
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 
 LPC21ISP_BAUD = 38400
@@ -40,21 +38,19 @@ GPS_PORT ?= UART0
 GPS_BAUD ?= B38400
 
 
-ADC_IR_TOP = ADC_0
-ADC_IR1 = ADC_1
-ADC_IR2 = ADC_2
-ADC_IR_NB_SAMPLES = 16
-ADC_GYRO_NB_SAMPLES = 16
+ADC_IR_TOP ?= ADC_0
+ADC_IR1 ?= ADC_1
+ADC_IR2 ?= ADC_2
+ADC_IR_NB_SAMPLES ?= 16
+ADC_GYRO_NB_SAMPLES ?= 16
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4017
-endif
+ACTUATORS ?= actuators_4017
 
 
 # All targets on the TINY board run on the same processor achitecture
diff --git a/conf/boards/umarim_1.0.makefile b/conf/boards/umarim_1.0.makefile
index 96980419b9..c48548d3d1 100644
--- a/conf/boards/umarim_1.0.makefile
+++ b/conf/boards/umarim_1.0.makefile
@@ -12,9 +12,8 @@ BOARD_VERSION=1.0
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
 
-ifndef FLASH_MODE
+# default flash mode is via usb bootloader
 FLASH_MODE = IAP
-endif
 
 
 LPC21ISP_BAUD = 38400
@@ -41,16 +40,13 @@ GPS_PORT ?= UART0
 GPS_BAUD ?= B38400
 
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4017
-endif
-
+ACTUATORS ?= actuators_4017
 
 # All targets on the Umarim board run on the same processor achitecture
 $(TARGET).ARCHDIR = $(ARCH)
diff --git a/conf/boards/umarim_lite_2.0.makefile b/conf/boards/umarim_lite_2.0.makefile
index 9f3d83de09..806bc7cfd3 100644
--- a/conf/boards/umarim_lite_2.0.makefile
+++ b/conf/boards/umarim_lite_2.0.makefile
@@ -11,11 +11,8 @@ BOARD_VERSION=lite_2.0
 
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
-
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
-
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 LPC21ISP_BAUD = 38400
 LPC21ISP_XTAL = 12000
@@ -42,16 +39,13 @@ GPS_BAUD ?= B38400
 
 
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4017
-endif
-
+ACTUATORS ?= actuators_4017
 
 # All targets on the Umarim board run on the same processor achitecture
 $(TARGET).ARCHDIR = $(ARCH)
diff --git a/conf/boards/yapa_2.0.makefile b/conf/boards/yapa_2.0.makefile
index e48927d112..0335aa7c5c 100644
--- a/conf/boards/yapa_2.0.makefile
+++ b/conf/boards/yapa_2.0.makefile
@@ -11,11 +11,8 @@ BOARD_VERSION=2.0
 
 BOARD_CFG=\"boards/$(BOARD)_$(BOARD_VERSION).h\"
 
-
-ifndef FLASH_MODE
-FLASH_MODE = IAP
-endif
-
+# default flash mode is via usb bootloader
+FLASH_MODE ?= IAP
 
 LPC21ISP_BAUD = 38400
 LPC21ISP_XTAL = 12000
@@ -40,22 +37,19 @@ GPS_PORT ?= UART0
 GPS_BAUD ?= B38400
 
 
-ADC_IR_TOP = ADC_0
-ADC_IR1 = ADC_1
-ADC_IR2 = ADC_2
-ADC_IR_NB_SAMPLES = 16
-ADC_GYRO_NB_SAMPLES = 16
+ADC_IR_TOP ?= ADC_0
+ADC_IR1 ?= ADC_1
+ADC_IR2 ?= ADC_2
+ADC_IR_NB_SAMPLES ?= 16
+ADC_GYRO_NB_SAMPLES ?= 16
 
-ADC_GENERIC_NB_SAMPLES = 16
+ADC_GENERIC_NB_SAMPLES ?= 16
 
 #
 # you can use different actuators by adding a configure option to your firmware section
 # e.g. <configure name="ACTUATORS" value="actuators_ppm/>
 #
-ifndef ACTUATORS
-ACTUATORS = actuators_4017
-endif
-
+ACTUATORS ?= actuators_4017
 
 # All targets on the TINY board run on the same processor achitecture
 $(TARGET).ARCHDIR = $(ARCH)